Spatio-temporal distribution of demersal fish species in the northern Alboran sea and Gulf of Vera
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1
Oceanographic Center of Málaga, Spanish Institute of Oceanography (IEO), Spain
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2
Centro Oceanográfico de Baleares, Instituto Español de Oceanografía, Spain
Fish species play an important role in ecosystems, influencing the flow of energy and sustaining a diversity of ecosystem functions. In the Mediterranean sea, demersal resources consist of a large variety of fish species, many of them considered target species of economic interest for fisheries. Thus, understanding the distribution pattern of most relevant species is essential to improve spatial management and ensure a long-term sustainable conservation of the species. In this study, interannual and spatial distribution (bathymetric and geographic) of 9 relevant fish species (Serranus hepatus, Boops boops, Pagellus acarne, Capros aper, Merluccius merluccius, Coleorhinchus caelorhinchus, Phycis blennoides, Nezumia aequalis and Galeus melastomus) of the Alboran sea and the Gulf of Vera was evaluated. These species constitute some of the most representative in the soft bottoms of the study area from 30-800 m depth. In addition, fishing effort was analysed and compared with the standardized abundance for the above mentioned species.
The study area ranged from Gibraltar to Cabo de Palos and corresponds to Geographic Sub Area 1 (GSA 1), according to the General Fisheries Commission for the Mediterranean Sea (GFCM). Data of fish fauna were collected from 1994, during 24 spring trawl surveys, as part of the MEDITS (International bottom trawl survey in the Mediterranean) project. The project use a randomised and stratified sampling design based on depth (five bathymetric strata: 10–50, 51–100, 101–200, 201–500 and 501–800 m). Catches were standardised to swept area (individuals•km-2) and data were pooled to obtain a matrix of species abundance by station. Bray–Curtis dissimilarity matrix was constructed to perform a non-metric multidimensional scaling (nMDS) analysis in order to identify species associations. Species abundance (x) were log (x+1) transformed to reduce the influence of dominant species. Analyses of similitude percentage (SIMPER) were used to identify those species that contributed to the similarity between groups of samples. The multivariate analyses were carried out using the PRIMER v6 (Plymouth Routines in Multivariate Ecological Research). Generalized additive models (GAM) were applied to assess the bathymetric, geographic and temporal effects on abundance using information at species level by haul. Year was considered as a factor. A one-dimensional smoother was used to investigate the bathymetric effect, while a two-dimensional smoother was used to account for the geographic effect, combining latitude and longitude. For the selection of the best model for each response variable, minimization of the Akaike information criterion (AIC) was applied. Fishing effort data, in terms of trips of trawlers per year, collected from 2003 to 2017, was analyzed. Correlation between fishing effort and abundance values of analyzed species was calculated using Pearson correlation coefficient. Fishing effort in the study area was compiled in the framework of the EU Data Collection Regulation (DCR).
We identified four assemblages being depth the main factor that determines the distribution of species: inner continental shelf (30-100 m), outer continental shelf (101-200 m), upper continental slope (201-500 m) and middle continental slope (501-800 m). According to the SIMPER analysis the most representative species (contribute more than 30% to the similarity in each assemblage) were: S. hepatus, B. boops and P. acarne for inner shelf; C. aper and M. merluccius for outer shelf; C. caelorhinchus and P. blennoides for upper slope; G. melastomus and N. aequalis for middle slope.
In every species (except B. boops), GAM analysis showed a statistically significant effect of depth and latitude-longitude on log-transformed data of abundance (p<0.01) (B. boops only showed for depth). The deviance explained ranged between 61.5 for M. merluccius and 91.4 for N. aequalis.
The bathymetric effect showed a non-linear pattern in all species analyzed, with abundance peaking between 30 to 100 m depth in S. hepatus, B. boops and P. acarne with decreasing trend below this depth; C. aper and M. merluccius showed maximum values at 200 m while C. caelorhinchus highest values were between 300-400 m. G. melastomus abundance increased from 200 to 600 m and N. aequalis from 300 to 600 m. Species were distributed heterogeneously throughout the entire study area. G. melastomus and N. aequalis abundance values were higher in Alboran Sea than in Gulf of Vera while opposite trends was showed by P. blennoides. The other species did not show a clear geographic pattern rather than a patchy distribution. Interannual variations in abundance values were highly heterogeneous and species-dependent. B. boops showed an increase of abundance from the first years to the rest of the time series. P. acarne abundance values decreased from 2013 to 2017. The other species showed high inter-annual fluctuation between 1994 and 2017 but no clear trend for the abundance index.
The examination of fishing effort showed that number of trips has declined with a statistically significant negative trend since 2003 (r=0.92; p<0.01). C. aper was the only analyzed species whose mean annual abundance values were negatively and significantly correlated with fishing effort (r=0.60; p<0.05). Regarding the other species, it has not been found increase or decrease on abundance values with reduction of fishing effect. Possibly a longer time series is required to reveal changes of these species.
In conclusion, it has been identified four assemblages in the study area being depth the main factor that determines the distribution of species. Results of GAM on abundance indices of 9 species selected based of contribution to the similarity in each of the identified assemblage showed that depth and location explain much of the variance explained. No increasing or decreasing trend has been identified but high inter-annual and independent variation was observed for most of species.
Acknowledgements
The authors thank all the participants in the MEDITS surveys. This study was carried out in the framework of DEMALBORAN and PESCAMED project. These projects has been funded by the Spanish Institute of Oceanography and the EU through the European Maritime and Fisheries Fund (EMFF) within the National Program of collection, management and use of data in the fisheries sector and support for scientific advice regarding the Common Fisheries Policy.
Keywords:
Demersal,
Mediterraenan sea,
Alboran sea,
Gulf of Vera,
distribution
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Poster Presentation
Topic:
Fisheries, Aquaculture and Biotechnology
Citation:
García-Ruiz
C,
Hidalgo
M,
Ciercoles
C,
Serna
JM,
Torres
P and
Gonzalez
M
(2019). Spatio-temporal distribution of demersal fish species in the northern Alboran sea and Gulf of Vera.
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00068
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Received:
29 Apr 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
PhD. Cristina García-Ruiz, Oceanographic Center of Málaga, Spanish Institute of Oceanography (IEO), Málaga, Spain, cristina.garcia@ieo.es